CRF's Only Forums

Hello Folks,

I'm finally getting around to my first time adjusting the valves on this bike and I've run into some issues. I watched quite a few Youtube videos (all with slightly different procedures) and none of them addressed the questions below. This is on a 2017 Honda CRF450RX that I purchased towards the end of last riding season and haven't really been able to ride this year at all b/c of how hard she has become to start. When I bought the bike, she started right up...but as the weather changed, she became harder and harder to start until she reached a place where it's nearly impossible to start right now. She starts up easier when the bike is warm...even leaving it out in the sunshine to help warm it up helps.

The previous owner did all his own maintenance and claimed that there was no need to adjust the valves on this bike (he may have been under that misconception b/c of the titanium thing...I honestly do not know)...so I'm working under the assumption that they've never been adjusted before. He stated they had not been...though he put at least 100 hours on the bike. I'd venture to say far more but he claimed the bike only had 90-100 hours on it and that they tore the bikes completely down each year to do maintenance on them (during our long winters here in the inland NW).

Here are my questions:

(1) Is it okay to remove the cam bracket BEFORE taking your reading??? I ask b/c I'm not sure if it's b/c of the size of my hands and the cramped space, the tools I'm using, or what, but I cannot take a reading unless I remove the cam bracket and hold the cam down with one hand while checking it with the other. Can you get an accurate reading by holding the cam down or do you need it bolted down when taking this measurement?

(2) My book specs the intake valves at .13mm +/- .03mm. As of this moment, I cannot an accurate reading on these as my smallest feeler gauge is .04. And, while I can get this gauge in, there's quite a bit of drag on it when I pull it out and I can actually feel the cam drop a tiny amount (with my other hand that's holding it down) when I remove it. How are you supposed to adjust these shims if you cannot get an accurate starting point/number???

(3) The book specs the exhaust valves at .28mm +/- .03. I currently have a reading of .25, so she's within spec. Should I attempt to get her closer to the .28 or just leave it alone, despite the fact that she's at MAXIMUM spec'ed values?

(4) If one was going to err, would you err towards getting the bike as close to the Specified clearance, or are you better off using the looser tolerance numbers? I don't want to cause any excessive wear...and I'd like to limit future wear as much as possible if I can. When shimming, which direction (up or down; lower or higher than the specified value) are you better off going with to avoid future wear and tear? Again, I have no idea if these have been adjusted before or not. That said, I've invested several grand in accessories for this bike, for the kind of riding I want to do, on top of what I paid for her, so I want to keep it as long as possible. I'm also NOT a fan of not having a kick start. I'd rather she had a carb, too, but that's beside the point. I just don't want to end up stuck way out in the back country b/c of electrical problems.

(5) I had a 5th question but lost it when I accidentally deleted my first post and had to retype everything. I will come back and add it after I remember what it was.

Thank you for any help I can get, Folks!!! I appreciate it greatly!

Good job making the effort to perform maintenance. That bike has been ridden a lot for its age, and could use the attention.

Buy the proper tools, like feeler gauges with the range you need. they are very cheap. Guessing when you are measuring to the 1/1000 of an inch or the mm equivalent is not possible. You could do more harm than good.

I would measure things with the cam arm on and torqued to spec. Who knows how much clamping force is provided, or what effect that has on the measurement?

I set my clearances at the tighter end of the spec. It is more gentle on the valve train to not slam together with loose clearances. I also has the effect of adding very very slightly more lift and duration to the cam. Whether there is a power increase would be extremely hard to measure.

You're not going to get to be a pro by doing this for the first time.

Good job making the effort to perform maintenance. That bike has been ridden a lot for its age, and could use the attention.

Buy the proper tools, like feeler gauges with the range you need. they are very cheap. Guessing when you are measuring to the 1/1000 of an inch or the mm equivalent is not possible. You could do more harm than good.

I would measure things with the cam arm on and torqued to spec. Who knows how much clamping force is provided, or what effect that has on the measurement?

I set my clearances at the tighter end of the spec. It is more gentle on the valve train to not slam together with loose clearances. I also has the effect of adding very very slightly more lift and duration to the cam. Whether there is a power increase would be extremely hard to measure.

You're not going to get to be a pro by doing this for the first time.

Thank you for the feedback. I don't reckon I'll ever be a pro at my age. I'm just getting back into dirtbikes after a 30 year hiatus...other than a ride here and there along the way. I do my own wrenching (what I can) on my Harley. I'm hoping to do the same with this bike. Thanks again!